docs: def get_propagator(name):
      """Retrieve a named propagator
  
      Args:
          name (str): Name of the desired propagator
      Return:
          Propagator class
      """
  
      from .sgp4 import Sgp4
      from .sgp4beta import Sgp4Beta
  
      scope = locals().copy()
      scope.update(globals())
  
      if name not in scope:
          raise UnknownPropagatorError(name)
  
      return scope[name]